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<title>The C Preprocessor: Other Directives</title>

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<a name="Other-Directives-1"></a>
<h2 class="chapter">8 Other Directives</h2>

<a name="index-_0023ident"></a>
<a name="index-_0023sccs"></a>
<p>The &lsquo;<samp>#ident</samp>&rsquo; directive takes one argument, a string constant.  On
some systems, that string constant is copied into a special segment of
the object file.  On other systems, the directive is ignored.  The
&lsquo;<samp>#sccs</samp>&rsquo; directive is a synonym for &lsquo;<samp>#ident</samp>&rsquo;.
</p>
<p>These directives are not part of the C standard, but they are not
official GNU extensions either.  What historical information we have
been able to find, suggests they originated with System V.
</p>
<a name="index-null-directive"></a>
<p>The <em>null directive</em> consists of a &lsquo;<samp>#</samp>&rsquo; followed by a newline,
with only whitespace (including comments) in between.  A null directive
is understood as a preprocessing directive but has no effect on the
preprocessor output.  The primary significance of the existence of the
null directive is that an input line consisting of just a &lsquo;<samp>#</samp>&rsquo; will
produce no output, rather than a line of output containing just a
&lsquo;<samp>#</samp>&rsquo;.  Supposedly some old C programs contain such lines.
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